The subject matter disclosed herein relates generally to isotope production systems, and more particularly to isotope production systems having a target material that is irradiated with a particle beam.
Radioisotopes (also called radionuclides) have several applications in medical therapy, imaging, and research, as well as other applications that are not medically related. Systems that produce radioisotopes typically include a particle accelerator, such as a cyclotron, that accelerates a beam of charged particles (e.g., H− ions) and directs the beam into a target material to generate the isotopes. The cyclotron is a complex system that uses electrical and magnetic fields to accelerate and guide the charged particles along a predetermined orbit within an acceleration chamber. When the particles reach an outer portion of the orbit, the charged particles form a particle beam that is directed toward a target assembly that holds the target material for isotope production.
The target material, which is typically a liquid, gas, or solid, is contained within a chamber of the target assembly. The target assembly forms a beam passage that receives the particle beam and permits the particle beam to be incident on the target material in the chamber. To contain the target material within the chamber, the beam passage is separated from the chamber by one or more foils. For example, the chamber may be defined by a void within a target body. A target foil covers the void on one side and a section of the target assembly may cover the opposite side of the void to define the chamber therebetween. The particle beam passes through the target foil and deposits a relatively large amount of power within a relatively small volume of the target material, thereby causing a large amount of thermal energy to be generated within the chamber. A portion of this thermal energy is transferred to the target foil.
Target foils experience elevated temperatures and pressures along the side of the target foil that borders the production chamber. The elevated temperatures and pressures cause stress that renders the target foil vulnerable to rupture, melting, or other damage. If the foils are damaged, the level of energy that enters the production chamber increases. Greater energy levels may generate unwanted isotopes or other impurities that render the target material unusable.
In addition, the target foils absorb energy from the particle beam. This energy might otherwise be useful for reactions within the production chamber. In addition, the target foils become highly activated over time and pose a health problem to technicians that must replace the target foils. The target foils may also contaminate the target media when the activated ions from the target foil are absorbed by the target material. Moreover, isotope production for at least some reactions may be better when the temperatures of the target material are less elevated.
To address the challenges of overheated foils, conventional systems include a cooling system that transfers the thermal energy away from the target foil. The cooling system directs a cooling medium (e.g., helium) through the cooling chamber that absorbs thermal energy from the foils. Despite the cooling system, however, the temperatures of the target foil and target material may still become excessive and other challenges, such as those described above, remain.